In the production of semiconductor wafers such as a silicon wafer, which is a typical example of a workpiece to be polished, double side polishing for simultaneously polishing the front and back surfaces of the wafers is generally employed to achieve more accurately controlled flatness quality and surface roughness quality of the wafers. The shape required for a semiconductor wafer (primarily the degree of flatness required for the whole surface and the periphery of the wafer) varies depending on the uses. It is necessary to determine the target amount of polishing of wafers depending on the requirements, and to accurately control the amount of polishing removal.
In particular, in recent years, due to miniaturization of semiconductor devices and increase in the diameter of semiconductor wafers, higher flatness are heavily required for semiconductor wafers subjected to light exposure. Against this background, techniques for accurately controlling the amount of polishing on wafers are strongly desired.
In this regard, for example, PTL 1 (JP 2002-254299A) discloses a method of controlling the amount of polishing on a wafer in accordance with the drop in the driving torque of polishing plates of a double side polishing apparatus during polishing.